Various types of hearing prostheses may provide persons with different types of hearing loss with the ability to perceive sound. Hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural hearing loss. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, including the cochlea where sound vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
Persons with some forms of conductive hearing loss may benefit from hearing prostheses, such as acoustic hearing aids or vibration-based hearing devices. An acoustic hearing aid typically includes a small microphone to detect sound, an amplifier to amplify certain portions of the detected sound, and a small speaker to transmit the amplified sounds into the person's ear. Vibration-based hearing devices typically include a small microphone to detect sound, and a vibration mechanism to apply vibrations corresponding to the detected sound to a person's bone, thereby causing vibrations in the person's inner ear, thus bypassing the person's auditory canal and middle ear. Vibration-based hearing devices may include bone conduction hearing devices, direct acoustic cochlear implants, or other vibration-based devices. A bone conduction hearing device typically utilizes a surgically-implanted mechanism to transmit sound via direct vibrations of the skull. Similarly, a direct acoustic cochlear implant typically utilizes a surgically-implanted mechanism to transmit sound via vibrations corresponding to sound waves to generate fluid motion in a person's inner ear. Other non-surgical vibration-based hearing devices may use similar vibration mechanisms to transmit sound via direct vibration of teeth or other cranial or facial bones.
Persons with certain forms of sensorineural hearing loss may benefit from cochlear implants and/or auditory brainstem implants. For example, cochlear implants may provide a person having sensorineural hearing loss with the ability to perceive sound by stimulating the person's auditory nerve via an array of electrodes implanted in the person's cochlea. The cochlear implant detects sound waves and converts them into a series of electrical stimulation signals that are delivered to the implant recipient's cochlea via the array of electrodes. Auditory brainstem implants may use technology similar to cochlear implants, but instead of applying electrical stimulation to a person's cochlea, auditory brainstem implants apply electrical stimulation directly to a person's brain stem, bypassing the cochlea altogether. Electrically stimulating auditory nerves in a cochlea with a cochlear implant or electrically stimulating a brainstem may enable persons with sensorineural hearing loss to perceive sound. It is also possible to stimulate in a hybrid fashion in the same ear such that acoustic amplification can be used to stimulate mildly-to-severely impaired hearing frequencies, while at the same time the cochlear implant stimulates the remaining severely-to-profoundly impaired frequencies. This configuration constitutes a “hybrid” implant device.
Persons with varying degrees of either type of hearing loss may benefit from a binaural or hybrid hearing prosthesis configuration. For example, a person with conductive hearing loss in the left ear and sensorineural hearing loss in the right ear may benefit from a binaural hearing prosthesis configuration in which an acoustic hearing aid is positioned in the left ear and a cochlear implant is implanted in the right ear. Moreover, a person with different degrees and/or types of hearing loss depending upon sound frequency in the same ear may benefit from a hybrid hearing prosthesis configuration in which a cochlear implant and another type of hearing prosthesis (such as an acoustic actuator or hearing-aid receiver) are positioned in the same ear, and another hearing prosthesis in the other ear.